The importance of clean semiconductor workpiece surfaces in the fabrication of semiconductor microelectronic devices has been recognized for a considerable period of time. Over time, as VLSI and ULSI silicon circuit technology has developed, the cleaning processes have gradually become a particularly critical step in the fabrication process. Trace impurities, such as sodium ions, metals, and particles, are especially detrimental if present on semiconductor surfaces during high-temperature processing because they may spread and diffuse into the semiconductor workpiece and thereby alter the electrical characteristics of the devices formed in the workpiece.
The actual stripping of photoresist from the workpiece is yet another fabrication process that is important to integrated circuit yield, and the yield of other workpiece types. It is during the stripping process that a substantial majority of the photoresist is removed or otherwise disengaged from the surface of the semiconductor workpiece. If the stripping agent is not completely effective, photoresist may remain bonded to the surface. Such bonded photoresist may be extremely difficult to remove during a subsequent cleaning operation and thereby impact the ability to further process the workpiece.
In order to produce a useful semiconductor wafer, first a silicon crystal is grown and then sliced into thin wafers. The thin wafers are then exposed to a photoresist which forms a layer on the wafers. Selected areas of the photoresist are exposed to light, which cures those areas. The remaining unexposed areas of photoresist are then etched off to form patterns on the wafers. Lastly, the wafers are cleaned.
There have been many attempts at improving the speed and efficiency of the removal of the photoresist. For example, Matthews, U.S. Pat. No. 5,776,296, discloses a process for removing photoresist from a semiconductor wafer by diffusing ozone (O3) into a bath of deionized water (DI) at sub-ambient temperatures of 1 to 15° C. to form a mixture (DIO3). However, the Matthews system and process suffers from certain disadvantages, most especially the low rate of removal of photoresist, as well as a requirement to chill the DI water with a chiller.
It is an object of the present invention to provide a faster and more efficient process of removal of photoresist from a silicon semiconductor wafer than any available in the prior art.
It is another object of the invention to provide an improved apparatus for use in the process which results in and efficient and fast method of removing photoresist from silicon semiconductor wafers.